WARSAW
— For the leading opposition party, Sunday's election here is the most important event since 1989, when Poland extracted itself from the Soviet Union while 250,000 troops were still in the country. They term it a historic battle between light and dark.

For center-right Civic Platform candidate Donald Tusk, Sunday's vote decides whether Poland turns inward, chauvinist, and authoritarian under Prime Minister Jaroslaw Kaczynski – or flowers into a more open economy and civil society, as well as a closer partner to Europe. The party also favors pulling Polish troops out of Iraq.

For Poland's ruling conservative Kaczynski brothers, who are president and prime minister, Sunday is a battle between light and dark, but for other reasons. For them, it is about establishing for the first time since the 18th century a genuine, "pure" Poland – a lighthouse of Catholic moral and Polish national virtues, a place where the forgotten poor have hope, and where the security services, rightly directed, will finally purge white collar crooks, communist collaborators, and ex-dissidents. Lech and Jaroslaw Kaczynski, the twins, as they are known here, want a Poland that stands for Poland in Europe, a friend of Washington, and isn't rolled over by Germany or Russia.

Until a week ago, most polls showed the Kaczynskis would take Sunday's election. But an Oct. 12 televised debate has put Mr. Tusk in a neck and neck race. European leaders, wondering about the direction of a new EU state often described as prickly or unpredictable, are very interested in the outcome.

The snap elections were called in August amid a terrific fracturing of political coalitions here. The atmosphere in Warsaw has been charged by a full-bore campaign by the Kaczynskis to dismiss high-ranking officials and even to imply that former dissidents like Solidarity leaders Lech Walesa, Bronislaw Geremek, and Tadeusz Mazowiecki, and even Polish war hero Wladyslaw Bartoszewski, a former foreign minister, are insufficiently patriotic.

Since taking office in 2005, the Kaczynski twins have fired or dismissed no fewer than 14 cabinet-level officials, including the ministers of finance, interior, defense, and foreign affairs. Defense minister Radek Sikorski, a prominent political figure here, resigned in February.

To be sure, experts admit that from the late 1990s to 2005, corruption in Poland was a serious problem. Yet the twins attempt to clean up Poland has been at least equally divisive. The combination of broad "lustration" laws this spring – that used old secret service files to ferret out collaborators (the effort was struck down by a constitutional court) – as well as the formation of an active secret bureau of investigation into corruption (beholden to the prime minister, according to Western diplomats) has created fear of retribution along political lines.

"The brothers use the anticorruption and the decommunization campaigns as two mutually reinforcing ways to vet anyone who wants to participate in public," says Jacques Rupnik of Sciences Po in Paris. "It has created a lot of hatred in Poland."

But the Law and Justice Party (PiS) of the twins appeals to ordinary people in the countryside, to older Poles who have not enjoyed the fruits of Poland's postcommunist economic success, and to staunch Catholics. "Kaczynski is not corrupt, and it is time to end our habit of business in politics," says Tomasz, a Warsaw taxi driver.

The Catholic voting bloc is potent. This is due, in no small part, to the media phenomenon of Radio Maryja. The radio outlet, which also includes a TV channel and several new schools, is an ultraconservative Catholic operation that analysts say can deliver some 2 million voters. Nearly all the leading political candidates have been on Radio Maryja.

But when Tusk, leader of the Civic Alliance (PO) Party said he wanted to take part in a Radio Maryja air discussion last week, a Law and Justice Party member of parliament, Jolanta Szczypinska, said: "In order to be invited by this radio station, [Tusk] would have to go to confession first."

Parties like the Civic Platform and the Left and Democrats (LiD), made up of an unusual blend of ex-communists and dissidents, score better in the cities and among what one Western diplomat called "the moving Poland" – younger, Internet-savvy Poles who identify themselves as modern and cosmopolitan.

Until this week, most polls showed that Law and Justice would dominate Sunday's vote.

Yet an Oct. 12 TV debate between Tusk and Jaroslav Kaczynski seems to have shaken the polls. Known as a "nice guy," Tusk, who has lost a number of Polish elections, took a combative approach with the fastidious Kaczynski – knocking his record, pointing out that Poland has built less than a mile of new roads in the past year, has not delivered on the leftist agenda of housing for the poor, and has harmed Poland's image in Europe.

But one of the big questions in Warsaw is whether Poles will show up to vote.

Many Poles have been tuning out a political process they see as tainted or obtuse. In the cities, the Kaczynskis are criticized as parochial or moralizing. The opposition is called hapless or message-less. While European states score 70 to 80 percent turnouts, Poland's recent election was closer to 40. A whopping 2 million of some 20 million Poles of voting age have "voted with their feet" since 2004, experts note, leaving for jobs in Europe, especially in London. Most are young.

"We spent 45 years painfully sacrificing to get the vote [during Soviet occupation] and now that we have it, no one uses it," says a Foreign Ministry official.

"As long as election turnout is only 40 percent, Polish politics will never be stable," says Radoslaw Markowski, at the Warsaw School of Social Psychology.

But as the race has tightened, some see hope. Currently, the two main contenders are within 5 points of each other in various polls.

"I don't think the democratic process is dead yet in Poland," comments a Western diplomat. "This is a real campaign."